Positive displacement internal combustion engines may be divided into many categories, two of which could be: fixed output and variable output engines. Especially for private vehicles, variable output engines are used in large numbers. This invention relates to variable output engines.
Power output is normally varied by varying the amount of charge combusted during each combustion cycle and by spacing the combustion cycles closer or farther apart time wise. For efficiency each of the varying amounts of charge combusted during each combustion cycle should be combusted under the following conditions:
1. Oxidizer to Oxidant Proportioning and Dispersion, air to fuel ratio. This should be right, so that all fuel molecules are completely oxidized, yet not too much air must be present, since too much air simply represents useless mass moved around a lot and expelled at higher temperatures than taken in thus carrying energy with it. Also excess air takes up space and this increases the combustion chamber volume decreasing the effectiveness of the conversion process; so do contamination products such as exhaust gas remnants. Contamination products block effective oxidization. Gasoline engines normally do have proper proportioning, either carburettored or fuel injected into the airstream. Diesels normally have poor proportioning under reduced output, since normally the amount of air entering is not throttled or regulated, because a full volume of air is required for raising the compression temperature sufficiently for ignition of the directly injected fuel.
2. The pure, properly proportioned and properly dispersed charge should be contained in a minimum relative volume of space upon ignition. Diesels score favourably here, but could be improved by proportionally reducing the amount of air and the volume of the chambers as the amount of fuel injected is reduced to vary power output. Normal gasoline engines score poorly in this respect. The weight of the properly proportioned and dispersed gas charge is varied to vary power output, but this varying weight is ignited in a fixed volume chamber, so that only at wide open throttle the actual compression pressure reaches permissible and efficient limits. Great improvement could be made by reducing the volume of the chamber in proportion to the weight of the gas charge admitted so that at all times, during varying power output, the charge is at maximum permissible pressure upon ignition.
3. The properly proportioned varying charge weight, as per item 1, compressed to maximum permissible values in each cycle, as per item 2, now must be expanded to near atmospheric pressures. This requires a varying length of stroke, as the charge weight is varied. Starting with a stroke length that is sufficient to fully expand the charge at full power output, the stroke length should be reduced as the weight of the gas charge becomes less when reducing power output, so that expansion below atmospheric pressure is avoided. Crank driven normal engines may have full expansion at a certain reduced power output, possibly at 25% of full power. Brayton cycle and axial and radial cam driven engines may have nearly full expansion at an output range which is near maximum, but there is the possibility that expansion to below atmospheric pressure occurs during low power output periods. Crank driven engines may be built which limit the charge by delayed opening or closing the intake valve, the limited charge may then be compressed to maximum permissible value in a chamber designed to accommodate this limited charge and the limited charge may thus be chosen to be such that it fully expands during the power stroke, but these remedies apply then only at full power output, and expansion to below atmospheric pressure becomes a possibility for low output periods. Ideally then, automatic means should be provided to avoid expansion below atmospheric pressure in the very low output range, if a large expansion ratio design is chosen, resulting in a constant geometric and gas expansion ratio but in a varying geometric volume for initial and final combustion chamber volumes. 4. Heat losses to the cylinder head, piston crown and cylinder walls should be avoided; with insulated cylinder heads and piston crowns probably being the most practical object. 5. Waste motion, especially of the heavy parts designed for combustion forces, such as pistons, rods, cranks, etc. should be minimized. Functions which can effectively be carried out by lighter auxiliary parts, such as exhausting, intaking and compressing, in other words, recycling functions, should be divorced from the heavy duty components where possible. In conventional 4 cycle engines, the pistons, con-rods and cranks are used for re-cycling functions, while in conventional 2 cycle engines the re-cycling is not carried out positively so that contamination of the charge, or adequacy of the charge, becomes a real problem. Ideally, therefore, any light duty re-cycling functions, which can be divorced from the heavy duty power train components without danger of contaminating or wasting the charge, should be divorced.
6. Friction losses are typically 8% of the generated mechanical power and are directly subtracted from it; they should be minimized. Carrying out light duty re-cycling functions such as intaking and compressing the fresh charge with fewer larger components which have less friction area and travel, improves the efficiency. Conventional engines using the power train components such as pistons, con-rods, cranks, for these purposes, generate considerable friction area and component travel; in excess what can be accomplished by fewer larger components.